1. Field of the Invention
This invention relates to implantable defibrillation and pacing leads and more particularly to devices of this type which employ fixation structure operative to engage and draw tissue laterally toward the distal end of the defibrillation or pacing lead.
The instant fixation devices are appropriate for minimally invasive defibrillation and use with new, deployable defibrillation leads which are implanted without the currently practiced thoracotomy procedures. The implantation of these leads requires making a small incision in the chest to gain access to the pericardial space. The defibrillation leads are then threaded through the incision and into the pericardial space either alone or through the lumen of a thin walled guiding catheter. Once initially placed in his fashion, a deployment action is performed to expand the surface area of the lead. At this point, the lead is generally held against the myocardial surface by the pericardium.
Because of the lubricious conditions which exist within that space, and the need to more precisely position the leads for defibrillation, lead fixation is required. Fixation to the pericardial sack is the safest approach since it completely avoids accidental laceration of the myocardial circulation. For additional safety, the instant fixation device utilizes hooks that penetrate through the pericardium and return to the lead. These designs do not leave a sharp, pointed object imbedded in the tissue. Still further, the fixation means needs to be robust in order to remain effective through the violent contractions experienced by the heart during initial defibrillation testing. Also, the ability to control device fixation using only simple axial, back-and-forth, "camera cable release-like" motions on common, off-the-shelf devices such as guidewires and stylets is highly desired. This is due, in part, to the fact that the lead may be partially or completely deployed and that lead body rotation and traction due to the remoteness of the insertion site may not be useful technique at this stage of the implant. It also should be noted that although the instant focus is pericardial fixation, these same fixation concepts can be applied to myocardial tissue if knowledge of the local circulation is accurate.
2. Description of Related Art
Various different forms of implantable and internally deployable defibrillation electrodes heretofore have been provided as well as hook and screw-type fixation devices for electro-catheters.
An internally deployable defibrillator electrode is disclosed in U.S. Pat. No. 4,860,760, but does not include structure for fixation prior to or subsequent to deployment of the electrode. U.S. Pat. No. 4,567,900 also discloses an internally deployable defibrillator electrode, but here again also is absent fixation structure.
U.S. Pat. No. 4,624,265 employs both rotary hook and rotary screw fixation devices for an electro-catheter, but rotary hook and rotary screw fixation devices which must be actuated by rotary torque applied at the proximal end of the electro-catheter are objectionable and, this patent does not disclose rotary hook or screw fixation devices which may be utilized in conjunction with an internally deployable defibrillator electrode.
U.S. Pat. No. 3,814,104 describes a pacemaker-lead which attaches to endocardial tissue by means of two gently curved hooks advanced from the lead by means of axial force applied by an internal stylet. The essentially straight hooks provide some degree of fixation but can allow the lead to be simply pulled from the tissue. Also, a special separate flexible catheter is required to force the hooks together if the device needs to be repositioned.
It is felt that the violent contraction of the heart which results from a defibrillation shock may cause the dislodgement of this or any easily removable lead. The need for additional, special hardware for repositioning is also unattractive.
U.S. Pat. No. 4,058,128 describes a pacemaker lead which attaches to the myocardium by means of a single, completely exposed barbed hook. At implant, a significant chest incision is performed to expose the pericardial surface, the lead is grasped with a special grasping tool, both the lead and grasping tool are introduced through the relatively large incision (compared to the lead body itself), the barbed hook is inserted into the myocardial tissue and the grasping tool is removed. In the event that repositioning is required, reintroduction of the grasper is necessary to reverse and then repeat the process.
It is felt that the surgical incision, and the need to introduce a grasping tool into the body, fail to adhere to the concept of a minimally invasive lead. Furthermore, a barb feature on this or any hook may also cause local tissue damage as a result of the violent contraction following the delivery of a defibrillation shock. Accidental laceration of the myocardial circulation is avoided, however, by undesired direct visual inspection of the implant through the large incision.
U.S. Pat. No. 4,013,690 describes a complex self-suturing, endocardial pacemaker lead and a special integral handle-stylet device permanently accompanying the lead from the time of manufacture. After the lead has been implanted using routine surgical technique, the handle activates the ejection of a thin, malleable wire through a distal tubular die and into the tissue. If the acute performance of the lead is satisfactory, the wire suture is broken at a predetermined separation point by means of rotation of the handle and the handle-stylet is removed. Any attempt the reposition this lead after this point would not be possible.
It is felt that this technology fails completely to provide a means to reverse the implant procedure and reposition the lead. Further, the violent contraction at defibrillation testing may weaken if not break the soft, malleable suture wire. Still further, as with '690, special and complex hardware is needed to accompany this lead.
U.S. Pat. No. 4,142,530 describes an epicardial pacemaker lead which is once again implanted through a significant incision in the patient's chest. Once positioned against the epicardium, the lead body is simultaneously pulled along and pressed onto the surface of the heart in order to engage the tissue in at least two curved pointed electrodes. This implantation requires the combination of lead retraction and compression by the surgeon. The means by which the compressive force is applied to the lead head is unclear. A straight, forward anchor is then activated by advancing a stylet against an internal feature of the anchor. This forward anchor generates a force which directs the curved electrodes against the tissue. A nylon wire is attached to the anchor to provide a means for the surgeon to retract the anchor.
It is felt that significant surgery would be necessary to implant such a device. Precise positioning of the electrode on the myocardium through a small incision may be difficult. Also, placement of a lead on the-posterior side of the heart may be impossible. Accidental laceration of the myocardial circulation by either the pointed electrodes or the anchor feature seems likely. The presence of the nylon wire would slightly increase the dimensions of the lead body. This wire becomes an unused, and unnecessary component remaining in the lead and therefore in the patient after the implant.
U.S. Pat. No. 4,233,992 discloses an endocardial electrode with a deployable helical hook. A provision is made to include a barb on these hooks. These leads are implanted using routine surgical technique. The first embodiment employs a non-reversible triggering element to deploy the hook. The second embodiment is deployed by means of a conically tipped stylet. Engagement of the heart tissue is accomplished by the application of external torque on the lead body by the surgeon.
It is felt that these devices fail to provide a means to reverse the implant procedure to accomplish repositioning or removal. Once either hook has been deployed, repositioning of the lead can be significantly hampered. Also, use of a barb may tear myocardial tissue due the contraction of the heart during defibrillation testing.
U.S. Pat. No. 4,357,946 teaches about an epicardial pacemaker lead which is to be implanted during thoracic surgery. Deployment of the helical screw fixation device is accomplished by means of rotation imparted by a stylet while the electrode head is in some fashion held upon the epicardial surface through an external force.
As with '128 and '530 above, it is felt that this technology fails to provide a device which can be implanted through a small incision. Moreover, a rotation action applied to the proximal end of a slim stylet is required to activate the fixation screw. The means to apply an external force to the lead head is unclear.
U.S. Pat. No. 4,378,023 discloses a percutaneously implanted myocardial electrode which blindly penetrates the myocardium to a significant depth. Fixation hooks are released within the myocardial tissue itself. External rotation is necessary to further deploy the fixation hooks. External traction is necessary to set the hooks into the tissue in at least one design.
It is felt that this technology fails on numerous counts. As with '530, precise placement of the electrode on the heart especially placement on posterior regions would be difficult if not impossible. Undesirable rotation of the lead to deploy the fixation hooks is required. Lead repositioning or removal would be extremely difficult. One embodiment in particular would require advancing the lead further into the myocardium to unset the hooks. Such a technique is completely blind and invites potentially lethal perforation of the heart.
U.S. Pat. No. 4,649,938 discloses an endocardial stimulating electrode which is implanted by means of routine surgical technique and requires the use of external rotation of the lead body to advance and attach helical screw to the tissue. Once fixed to the tissue, the spring-loaded helical screw holds the tissue in close proximity to the electrode.
It is felt that this technology fails to accomplish the goals of the instant invention because of the necessity to rotate the entire lead body to engage the tissue. Also, the combination of this undesirable lead body rotation and application of axial force to overcome the spring bias complicates the implant procedure.
U.S. Pat. No. 4,858,623 discloses an endocardial pacemaker lead which deploys a simple spring loaded hook from the lead by means of an axial force applied to an internal stylet. Once deployed, the lead engages tissue following application of external rotation imparted to the lead body. If repositioning is necessary, the stylet is further advanced to locate the hook in its most distal position. The lead is then pulled free of the tissue by simple traction.
If is felt that this technology fails to accomplish the goals of the instant invention because lead body rotation is necessary to attach the lead to the tissue. Also, as with '104, the ease of tissue disengagement by means of simple traction is an undesirable characteristic of a defibrillation lead.